This invention relates generally to ultrasonic testing systems, and more particularly, to an ultrasonic wheel detector for rolling along a specimen to be tested for flaws having a plurality of ultrasonic acoustic transducers and an acoustic barrier emersed in a coupling fluid.
The prior art has thrust at the problem of ultrasonically testing long specimens of metal objects by providing ultrasonic acoustic wheel probes which are filled with a coupling fluid and which roll along the specimen to be tested. One early ultrasonic wheel probe is described in U.S. Pat. No. 3,628,375 which issued to the applicant herein on Dec. 21, 1971. The structure described in this reference utilizes an ultrasonic transducer immersed in the coupling fluid within the annular container which forms a wheel. The ultrasonic transducer is adjustably mounted so as to be obliquely movable to control its inclination and consequently the angle of incidence of the ultrasonic energy with respect to the plane normal to the surface of the material against which the wheel is rolling. In this known system, the transducer is of the type which converts electrical signals into acoustic energy which is propagated through the coupling fluid and into the specimen being tested for flaws, and receives reflected acoustic energy which is converted back to electrical signals. It is a characteristic of such a single transducer system that considerable interface echoes are received, thereby reducing the resolution capability of the system, which in turn results in a system unable to inspect 100% of the thickness of the material under test.
The use of dual transducers, one for transmitting ultrasonic energy and the other for receiving the echoes, without an interface echo, allows the system to test and gate a specimen completely from the front surface of the specimen all the way to the back wall of the specimen material. PG,3 It is, however, a problem with the use of dual transducers within a wheel filled with coupling fluid that the acoustic energy will propagate through the coupling fluid from the transmitting transducer to the receiving transducer, directly. This results in objectionable crosstalk which adversely affects the detection process. A dual transducer system, however, provides the advantage that the return echoes are received on a propagation axis which is away from the transmission axis along which is propagated the main excitation pulse. Also the returning echo to the receiver transducer is that of a boundary reflection beyond the front surface of the specimen under test.
Dual transducer testing systems are described in U.S. Pat. Nos. 4,165,648 and 4,174,636 which issued to the applicant herein on Aug. 28, 1979, and Nov. 20, 1979, respectively. In each of these known systems, isolation between the transmitting and receiving transducers is achieved by providing a separate fluid coupled wheel for each. The wheels are coupled to one another by an adjustable coupling arrangement which permits variation of the spacing between the wheels. In this manner, the dual wheel system can be adapted to accommodate specimens to be tested having different thicknesses. Inter-wheel spacing is adjusted automatically by a servo system which is responsive to a thickness-measuring transducer. The ability to use two separate wheels in dual mode operation is possible because the waves propagating through the test piece are in sheer mode allowing much steeper return angles than exist in a longitudinal mode of operation. Clearly, this known arrangement is complex and expensive. Also this known arrangement is limited to a shear wave transducer mode. It is impossible to use two fluid coupled wheels in a longitudinal mode of operation due to the physical dimensions required.
It is, therefore, an object of this invention to provide an ultrasonic wheel probe which is inexpensive and which can introduce ultrasonic acoustic energy into an elongated specimen to be tested for flaws or to determine thickness.
It is another object of this invention to provide an ultrasonic probe which can receive ultrasonic acoustic energy echoes from a specimen being tested for flaws.
It is also an object of this invention to provide an ultrasonic probe wherein transmitted ultrasonic acoustic energy is transmitted and echoes thereof are received via a confined liquid transmission medium interposed between a specimen being tested and the transmitting and receiving transducers.
It is a further object of this invention to provide a liquid immersion wheel probe wherein crosstalk communication between transmitting and receiving transducers via the liquid transmission medium is prevented.
It is additionally an object of this invention to provide an immersion-type ultrasonic probe wherein the liquid transmission medium is confined in a deformable container which is deformed in response to changes in the contour of the specimen being tested for flaws.
It is still a further object of this invention to provide an immersion-type wheel probe wherein crosstalk communication between transmitting and receiving transducers through the liquid medium is prevented notwithstanding deformation of the deformable container.
It is still another object of this invention to provide a fluid-filled acoustic wheel probe wherein changes in the distance between the transducers and a surface of the specimen being tested for flaws are monitored.
It is yet still an additional object of this invention to provide a wheel probe wherein the orientation of the transducers with respect to the specimen being tested for flaws is adjustable to permit testing of specimens of various thicknesses.
It is yet a further object of this invention to provide an ultrasonic acoustic probe wherein return echoes are propagated through a transmission medium along a different propagation axis than the original transmission.
It is yet a still further object of this invention to provide an acoustic testing arrangement using dual wheels and having improved accuracy and an increase in the testing range within a given specimen thickness.
Another object of the invention is to provide an ultrasonic wheel probe wherein transmitting and receiving transducers can be oriented to focus at a depth within the specimen being tested where flaws are suspected to be incurred.
Another additional object of the invention is to provide an acoustic probe system wherein normal echoes from the surface of the specimen being tested are monitored to determine a distance between a transducer and the surface.
An additional object of the invention is to provide an electronic gating system responsive to surface echoes from the specimen being tested for flaws and which monitors the actual transducer position in relation to the surface of the specimen.
An additional object of the present invention is to provide an ultrasonic acoustic probe arrangement having a high signal-to-noise ratio between plural transducers.
Additionally, it is an object of this invention to provide an ultrasonic acoustic wheel probe having separate transmit and received transducers.
Also, it is an object of this invention to provide an ultrasonic acoustic wheel probe arrangement which can couple dryly to specimens to be tested for flaws.